Inkjet digital printing device and ink reservoir

ABSTRACT

The present invention relates to a digital device for printing on “open” or “closed” surface substrates by demand bubble-jet comprising at least one built-in ink reservoir ( 13 ) with a system of anti-splash partitions, at least one printhead and one buffer reservoir, the whole located in a print module ( 1 ) which moves in relation to the substrate ( 5 ), characterized in that it The device comprises a means for creating, during operation of the module, on the one hands a vacuum in the built-in reservoir, with a method of active regulation of this vacuum by adjustment of the ink level detected by a sensor attached to the built-in reservoir and on the other hand, the air pressure in the built-in reservoir.

The present invention relates to a digital printing device operating byspraying ink onto a substrate, which may have either an “open” in otherwords absorbent surface such as for example paper or cardboard, or a“closed” in other words non-absorbent surface such as for example someplastic materials or glass. The principle of this so-called ink jettechnology consists in spraying fine ink drops onto the substrate in amatrix based pattern, so as to print characters or graphics from digitaldata.

This printing principle has been in use since about the 1970s in respectof black and white and since the 1980s in respect of color printing.Applications exist in particular in the field of high-speed printing,low-cost color printers for personal computers, or industrial printingon a variety of substrates. The present description applies to printingon any substrate, <<open>> or <<closed>>, for example by a machine forcustomizing plastic cards or other portable objects, but it is obviousthat such an invention may also apply to a number of other cases.

In the case of industrial machine printing, printing is carried out by aprinthead including one or more electronically controlled print nozzlessupplied by a reservoir containing ink in liquid form. These nozzles areable to operate according to a “Drop or Dot On Demand” principle, thesedrops being released for example by piezoelectric effect. Other systemsoperate according to the “deflected jet” principle, whereby an ink jetis propelled permanently towards the substrate, and whereby electricallycharged electrodes deflect this jet into a gutter at times when printinga dot is not required. The unused ink is recovered and sent back to theink reservoir.

These components are combined in a print module which moves over theprint substrate so as to cover the whole required print surface whilebeing connected to a fixed control bay. This unit may constitute one ofthe stations of a machine or a line of machines for producing andcustomizing plastic cards or other portable objects.

On machines intended to work at high speed, for example more than 2000cards per hour, the print module moves at a speed which is sufficientlyhigh for the liquid ink contained in the reservoir to presentsignificant splashing or agitation. Such agitation may give rise to anumber of drawbacks: a variation in ink height and therefore in pressureand therefore in size of the ink drops deposited on the substrate,formation of bubbles in the reservoir, lack of ink coming from theoutlet hose even if the reservoir is not empty, difficulty in getting avalid measurement of the ink level in the reservoir.

The objective of the present invention is to overcome one or moredrawbacks of the prior art.

In this respect, the invention proposes a digital device for printing on“open” or “closed” surface substrates by demand bubble-jet comprising atleast one built-in ink reservoir with a system of anti-splashpartitions, at least one printhead and one buffer reservoir, the wholelocated in a print module which moves in relation to the substrate,characterized in that it comprises means for creating, during operationof said print module, on the one hand a vacuum in the built-inreservoir, using active regulation means for regulating this vacuum byadjustment of the ink level detected by a sensor attached to thebuilt-in reservoir and on the other hand, the air pressure in thebuilt-in reservoir required for printhead cleaning phases.

According to a particularity, the device is characterized in that itcomprises means for pressurizing the air in the reservoir for cleaningthe printhead nozzle(s).

According to a particularity, said active regulation means comprise anon-contact sensor measuring the level, without contact with the ink,through a wall of the built-in reservoir, the said sensor beingconnected to means for cutting off the ink flow by interrupting thesupply of ink to the built-in reservoir, said means of cut-off beingcontrolled by a circuit receiving level signals from the non-contactsensor in order to regulate the level of ink in the reservoir.

According to a particularity, said active regulation means for activelyregulating the vacuum comprise a pneumatic system consisting of meansfor measuring the amount of vacuum and means for creating a vacuum, thepressure of which is controlled by an electronic circuit according tosignals from the level sensor, ink system supply solenoid valve controlsignals and air system solenoid valve control signals.

According to a particularity, said means for creating a vacuum use theventuri effect.

According to a particularity, said means for creating a vacuum include aregulated vacuum pump.

According to a particularity, said print module comprises a “buffer”reservoir which can store a certain quantity of air at high or lowpressure, this buffer reservoir smoothing out the pressure variationsoccurring in the pneumatic system.

According to a particularity, said built-in reservoir forms a storagespace which contains several separators dividing this storage space intoseveral areas covering the full height or part of the height of thereservoir, these areas having a horizontal section of the order of 1cm², to reduce splashing of the ink.

According to a particularity, said separators comprise a number ofinter-locked vertical partitions.

According to a particularity, the device is characterized in that forthe nozzle cleaning phase, a flexible blade is placed in position incontact with the head equipped with the nozzles and means of movementcause the head to move in relation to the flexible blade in such amanner as to wipe the nozzle plate.

According to a particularity, the device is characterized in that aprint module moves in relation to a stationary control bay and at leastmost of the compressed air used in the print module comes from thecontrol bay via at least one flexible hose having sufficient length toallow movement of the print module.

According to a particularity, the device is characterized in that saidwall of the ink reservoir comprises a thinner part near the sensorenabling improved operation of the ink level sensor through this thinnerpart, the reduction in thickness being such that the thickness of saidwall at this point is less than 1 mm.

According to a particularity, at least one printhead carries a pluralityof print nozzles arranged in a row inclined at an angle to a plane atright-angles to the direction of travel of this printhead in relation tothe print substrate, and in that it includes means for adjusting thisangle, said means of adjustment determining several preset positionsenabling a change from one to another without requiring furtheradjustment of the angle and without altering the adjustment of thesepreset positions.

According to a particularity, said various preset positions correspondto angled positions making it possible with the same spacing of theprint nozzles on the printhead to print according to preset resolutionsby varying the spacing of the dots printed on the substrate, the spacingdecreasing as the angle increases.

According to a particularity, said means of movement move at least one“cleaning” blade, which can be soaked in a solvent or rubbed on anabsorbent felt before scraping the printhead, and the means of movementmove at least one other “wiping” blade, scraping the outer surface ofthe printhead after the passage of the cleaning blade.

According to a particularity, the device is characterized in that itincludes a data processing system known as a control system, receivingsignals from at least one ink level sensor or pressure sensor or both,controlling the compressed air supply pressure adjustment equipment orthe cut-off equipment or the distribution equipment or the non-returnequipment or a combination of these components, via at least oneelectronic interface.

According to a particularity, the device is characterized in that theprint module includes an electronic interface communicating with thecontrol system via a series connection.

According to a particularity, the device is characterized in that itincludes a drain tray, brought in front of the head to receive inkejected from the head during purging operations.

The invention, with its characteristics and advantages, will becomeclearer from reading the description given with reference to theappended drawings in which:

FIG. 1 shows a diagrammatic view of the device according to theinvention in one embodiment;

FIG. 2 shows a side view in vertical cross-section of a built-in inkreservoir of the device according to the invention in one embodiment;

FIGS. 3 a and 3 b show a view from above in horizontal cross-section ofa built-in ink reservoir of the device according to the invention in anembodiment comprising an anti-splash device in the form of inter-lockedand honeycomb partitions respectively;

FIG. 4 shows a cross-sectional side view of a cleaning station of thedevice according to the invention in one embodiment;

FIG. 5 shows a view from above of the print nozzle positions in relationto the print substrate during a passage of a printhead in respect of adevice according to the invention in one embodiment;

FIGS. 6 and 7 show respectively a partial view in side cross-section andin underneath cross-section of the print module part bearing theprinthead.

The following description applies to a device for printing a chip cardusing a process operating a “drop on demand” mode, but may also applyfully or in part to a device operating in “deflected ink jet” or otheroperating modes, as well as to any other type of substrate, with both an“open” or “closed” surface.

In one embodiment the print device according to the invention iscomposed of a stationary part (2) called the control bay and a movingpart (1) called the ink jet print module of the Drop On Demand type,controlled in a known way and which carries one or more printheads (14).Each printhead comprises one or more print nozzles (141) of a knowntype, distributed in a matrix figure able to include for example 128 or500 nozzles over a width of a few centimeters.

In another embodiment (not shown), the print substrate moves duringprinting while the print module is stationary.

The unit can be incorporated into a production or customization line,and be programmed to print text or images on a substrate (5) with an“open” or “closed” surface, for example constituted by a plastic card orany other portable object, brought on a conveyor in front of the controlbay (2) or under the print module (1). Each time a new substrate is inposition, the print module passes one or more times according to thesurface to be printed and the width of the printhead. The nozzles arecontrolled electronically and individually in order to spray ink dropsonto the substrate, and therefore to print marks for example in the formof dots, as the module moves over the substrate or as the substratemoves under the module, and as a function of this movement.

According to the applications, it is possible to fit to the device oneor more print modules able to print in juxtaposed or overlapping mode,in one or more colors.

According to the applications, it is also possible to fit to a printmodule one or more heads positioned relative to each other for examplein order to print in juxtaposed or overlapping mode, in one or morecolors.

According to the applications, it is also possible to connect eachprinthead to one or more built-in reservoirs, for example so as to beable to replace or clean a reservoir without stopping the printing forany length of time.

According to the applications, it is also possible to connect eachreservoir to one or more printheads, for example to increase the printwidth that can be achieved with each color.

The present invention applies to a device including a single printmodule (1) that bears a single built-in ink reservoir (13) and a singleprinthead, but its characteristics may be applied to other combinationsof these elements without departing from the spirit of the invention. Inthe same way the different functions of the device are described asbeing controlled by the same computerized control system (3) using anelectronic interface (31) located in the print module (1), but may alsobe managed by several different systems or interfaces, or a combinationof these elements, without departing from the spirit of the invention.

The printhead (14) uses print nozzles (141) spraying a drop of ink ondemand via a piezoelectric actuator. In an operation of this type, thereservoir of liquid ink supplying the printhead is kept at a slightlylow pressure relative to the ambient pressure, in such a way that thenozzles allow no ink to escape without an actuator command. On the otherhand, to purge the nozzles before a prolonged stoppage or to unblockthem in the event of a problem, the reservoir may be subjected to highpressure, for example of about 0.5 bars.

In an embodiment shown in FIG. 1, the printhead (14) is supplied withink by a built-in reservoir (13). This built-in reservoir is suppliedthrough a flexible hose (c20) by a main reservoir (23) pressurized by asource (A) of compressed air of a known type by means of a pressureregulator (21 c), this same main reservoir (23) being located in thecontrol bay (2) and fitted with a level sensor (28) connected to thecontrol system (3) to deliver a level signal. The ink level in thebuilt-in reservoir (13) is regulated by the control system (3), by meansof the electronic interface (31), acting on cut-off means (17) includinga solenoid valve closing the ink passage upstream of said built-inreservoir (13). This regulation is carried out from signals supplied byat least one non-contact capacitive effect ink level sensor (18) locatedon the built-in reservoir (13).

In one embodiment, a source of compressed air (A) supplies a part of thepneumatic system located in the control bay (2) through adjustment means(21 a, 21 b), for example pressure regulators, controlled in associationwith pressure measurement means (22 a, 22 b) by the control system (3).

These pressure measurement means (22 a, 22 b) may include pressureswitches directly or indirectly controlling the pressure adjustmentmeans (21 a, 21 b), which may be composed of pressure regulators. Thesepressure measurement means may also be simple pressure sensorstransmitting a value to the control system (3), which controls theadjustment means (21 a, 21 b).

These means are controlled in order to deliver to the print module (1) aflow of compressed air at a set pressure through a first hose (c10 a)and a second hose (c10 b), the pressures and flows in these two hosesbeing able to be different.

The first hose (c10 b) coming from the control bay (2) suppliescompressed and regulated air to a venturi effect vacuum generator (12)of a known type, located in the print module (1), which vacuum generator(12) imparts a slight vacuum to a part (c12) of the pneumatic system(c1) in this same print module.

The print module (1) includes distribution means (15), such as asolenoid valve, controlled by the control system (3) by means of theelectronic interface (31). According to need, these distribution meansbring the built-in reservoir (13) into communication with either thevacuum part (c12) of the pneumatic system, or the high pressure part(c13) located in the print module which is supplied with compressed andregulated air by the second flexible hose (c10 b) coming from thecontrol bay (2).

A computerized system (3) uses the signals coming from the differentpressure sensors or pressure switches and controls the pressureregulators so as to maintain, outside head cleaning phases, in thebuilt-in reservoir (13) a vacuum the value of which is calculated so asto be sufficient to retain the ink in the nozzles in normal operationwithout preventing its ejection by the piezoelectric actuator. In orderto be free from variations in atmospheric pressure and to avoid theadjustments which might arise from them, the control system (3) may beprogrammed so as to maintain a vacuum in the built-in reservoir (13)such that the difference in pressure between the inside and the outsideof said reservoir is stabilized at a known and independent ink levelvalue.

Stabilizing this difference in pressure makes it possible to ensure thatthe size of the drops and therefore of the printed dots is regular andforeseeable, which is important in order to ensure print quality andregularity, both in time and when changing substrates, or substratetypes for example between “open” and “closed”.

The pneumatic system in the print module (1) includes non-return means(16), such as one or more controlled valves, or one or more clacks, or acombination of these components. These components of a known type areconfigured or controlled so as to seal the air inlet of the built-in inkreservoir (13) hermetically in the event of a drop in pressure due to aproblem.

In one embodiment, the pneumatic system in the print module (1) includesa buffer reservoir (11) located between the distribution means (15) andthe built-in reservoir (13). This reservoir may contain a certainquantity of air at high pressure or low pressure, and thus allowspressure levels in the built-in ink reservoir (13) to be regularized forexample during an inflow of ink or in the event of irregularities in thesupply of compressed air to the print module (1), or when there arevariations in pressure caused either by the drop in the ink levelthrough use, or by the rise in the level during re-filling.

By way of example and in one embodiment, the capacity of the bufferreservoir (11) is about 25% of the internal volume of built-in inkreservoir (13).

In the embodiment shown in FIG. 2, a vertical wall of the built-inreservoir (13) of the print module (1) has in its lower part a thinnerpart (131) of an electrically non-conductive material. In this thinnerpart and outside the reservoir is housed a non-contact electronic sensor(18) for example with a capacitive effect of a known type, connectedelectronically to the control system (3) or to the electronic interface(31) or a combination of the two. By a variation in the signalrepresenting the electrical capacity of the sensor, due to the presenceor not of liquid on the other side of the wall, the control systemdetects the fact that ink level in the built-in reservoir (13) is belowa set height corresponding to the position of this ink level sensor(18).

The thinner part (131) is such that the wall of the reservoir has athickness of about 1 mm, for a wall of Nylon™ or Delrin™.

This ink level signal is used by the control system (3), for example soas to control the opening of the cut-off means (17) and to allow the inkto inflow into the built-in reservoir (13) coming from the mainreservoir (23) as soon as the sensor detects that there is no longersufficient ink. When the ink reaches the reservoir, the control systemwill be able to interrupt this inflow of ink as soon as the sensor againdetects the presence of a required ink level.

The frequency of the ink supply cycles of the built-in ink reservoir(13) is reduced owing to the existence of a hysteresis loopcharacteristic of the level sensor (18), and the use of a time delay intaking account of sensor signals of for example 0.5 seconds, in order toavoid taking account of oscillations of level due to splashing in thereservoir.

Given its position outside the reservoir, the presence of this ink levelsensor (18) causes no sealing or ink pollution problems and it is easyto clean; and since it operates without heating it causes nodeterioration in the quality of the ink contained in this samereservoir, in particular when the ink used is in fact selected to beheat sensitive in respect of certain applications.

In one embodiment, the main ink reservoir (23) of the control bay (2)carries an ink level sensor (28) of the same type. This sensor (28) isconnected electronically to the control system (3). By this ink levelsensor (28), the control system (3) detects the fact that the ink levelin the main reservoir (23) is below a pre-set height corresponding tothe position of this ink level sensor (28). This signal is used by thecontrol system (3) for example to warn a human operator of the need foran imminent re-supply of ink.

The built-in ink reservoir (13) shown in FIGS. 2 and 3 a is in the shapeof a parallelepiped receptacle the upper opening of which is closed by alid fitted with sealing means such as a rubber seal (137).

In its lower part, the built-in ink reservoir (13) comprises an inkoutflow opening (139) connected to the printhead (14) and supplying inkto the latter.

The upper lid comprises an air passage opening (138) connected to thepneumatic system in the print module (1). This connection allows theinner space of the reservoir to be put under vacuum or under highpressure respectively according to the adjustment of the distributionmeans (15), in order on the one hand to compensate for ink pressure dueto gravity and to retain the ink in each print nozzle (141) of theprinthead (14) between two triggerings of the actuators of said printnozzles and respectively on the other hand to drain or unblock thisreservoir (13) or said print nozzles (141) or the hoses connecting thereservoir (13) to the nozzles during cleaning phases.

In order to reduce ink agitation inside the built-in reservoir (13), theinner space of said reservoir is separated into several areas (130) byseparators (132) constituted of inter-locked vertical partitions, thesepartitions being for example molded with the reservoir or subsequentlyadded to it. These partitions occupy the inner space of the reservoirover a large part of its height while leaving free a space (133 a)located at the bottom of this same reservoir and a space (133 b) locatedat the top of the reservoir. In this way, these partitions prevent orrestrict all horizontal circulation within the reservoir during itsmovements, except in its lower part (133 a) where the ink is able tocirculate so as to distribute itself throughout the areas (130) of theinner space of this built-in reservoir (13). In the upper part of thereservoir, the free space (133 b) above the separators (132) allows theair to circulate so as to distribute itself throughout the areas (130)of the inner space of this built-in reservoir (13).

The part of the height of the inner space of the built-in ink reservoir(13) occupied by the separators (132) may vary according to theapplications. By way of example and in one embodiment, the separators(132) occupy more than 75% of this height. According to the application,the separators (132) may comprise at various points up their heighttransverse drilling which increases the ink circulation possibilities.

The areas (130) delimited by the separators (132) are of sufficientlysmall cross-section for the differences in ink height from the splashingcaused by movements of the reservoir to be less than a given value, forexample 10 mm. In one embodiment, the distance between the partitionsconstituting these separators (132) is about 6 mm.

The upper lid also comprises an ink inflow opening (135) receiving thepressurized ink from the main reservoir (23) of the control bay (2)through a flexible hose (c20) and the ink inflow cut-off means (17).

An anti-splash device of this kind makes it possible to use fast headmovement (14) and therefore print speeds, without causing agitation orsignificant ink level variations in the reservoir, which might causevariations in static or dynamic pressure between the different nozzles(141) of the head or over time, and therefore irregular sizes for thedrops and dots printed on the substrate.

In the embodiment shown in FIG. 2, the ink inflow (135) emerges above aninclined plane formed in the inner wall of the built-in ink reservoir(13). The upper surface of this inclined plane forms a debulking surface(136) onto which the ink flow will run slowly before reaching the inkstorage space (E) already present in this same built-in reservoir. Theshape, the inclination, or the dimensions of this debulking surface(136) may vary according to the applications, and are determined in sucha way that bubbles which may be present in the ink when it flows in maydisaggregate as the ink flow runs along this same debulking surface(136) or as it runs from this same surface to the reservoir storagespace. In another embodiment (not shown), the ink inflow opening (135)in the built-in ink reservoir (13) may be located on a vertical wall,and the ink flow comes into contact with a debulking surface located inthe same wall or opposite this ink inflow.

In another embodiment (not shown) the debulking surface (136) is formedof the peripheral surface of an approximately cylindrical wire,connecting the ink inflow (135) to an inner wall of the built-inreservoir (13) or to a separator (132). The ink flow encounters the wirewhen it reaches the reservoir, and runs along its surface until it meetsthe ink (E) already present in this same built-in reservoir.

The built-in ink reservoir (3) in FIG. 2 shows on one of its outersurfaces a channel, blocked by a lid (111) equipped with sealing means(112). The inner space of this channel is connected to the air system ofthe print module (1) by an air passage opening (113) and constitutes abuffer reservoir (11), which allows the pressure inside at least onepart of said air system to be regularized.

In an embodiment shown in FIG. 3 b, the separators (132) separating theinner space of the built-in ink reservoir (13) are mainly constituted bya “honeycomb” shaped structure the conduits of which are orientatedvertically and provide a free space at the bottom of the reservoirallowing a distribution of the ink between the different conduits ofthis structure. According to the applications, the “honeycomb” structuremay comprise at various points up its height transverse drilling whichincreases the horizontal ink circulation possibilities.

In an embodiment shown in FIG. 4, the device according to the inventionmay include a cleaning station (24) to which the printhead may bebrought at a command from the control system (3), either by movement ofthe printhead (1), or by movement of said cleaning station (24), or by acombination of the two.

The cleaning station (24) includes a drain tray (240), fitted with anoutlet, receiving the ink ejected by the print nozzles (141) at a draincommand, in order for example to clean or unblock said print nozzles.

The cleaning station (24) includes a tray containing a solvent (S) andis equipped with a first resilient rotary so-called cleaning blade(241). At a command from the control system (3), this cleaning blade issoaked in the solvent (S) then rotates in order to scrape the outersurface of the printhead (14), for example to unblock the print nozzles(141) after a prolonged stoppage or to clean these same nozzles after adrain operation.

The cleaning station (24) is fitted with a second resilient so-calledwiping blade (242). At a command from the control system (3), thiswiping blade scrapes the outer surface of the printhead (14), in orderfor example to wipe or dry the print nozzles (141) after a passage ofthe cleaning blade (241). This device also removes any vestiges of dirtwhich might be left from the previous scraping.

In one embodiment the cleaning station (24) is fitted with elevationmeans (not shown), for example in the form of a rack and pinionmechanism, bringing this same cleaning station to the level of the lineof movement of the print substrates, and allowing a cleaning of theprinthead (14) without disassembly of the latter.

In the embodiment shown in FIGS. 5, 6, and 7, the device according tothe invention includes a printhead (14) the print nozzles (141) of whichare arranged in one or more rows parallel to each other, and the nozzlesof a same row have between them a pre-set spacing (e1) according totheir alignment in the row.

In order to be able to modify the print resolution, the printhead (14)is integral with a moving part (192) rotating relative to a stationarypart (191) integral with the print module (1), this rotation occurringaround an axis of inclination (d19) perpendicular to the plane of theprint substrate (5).

The printhead (14) may then be positioned in such a way that the rows ofprint nozzles (141) form a pre-set angle (as) called a “slantage” anglewith a plane perpendicular to the direction (d14) of relative movementof this printhead (141) over the substrate (5) during a print phase. Inthis way, the dots (541) printed on the print substrate (5) have betweenthem a clearance (e5) smaller than the spacing (el) existing between theprint nozzles (141). Such an arrangement thus makes it possible toincrease the print resolution achievable with a given printhead, inother words the number of dots printed over a given length or surface.

The moving part (192) of the head has a convex surface (196) of conicalshape engaging with a complementary concave surface (197) carried by thestationary part (191) in order to guide this same moving part (192) inrotation along the axis of inclination (d19). The moving part (192) alsohas a part forming a shoulder (198), directed towards the printsubstrate (5). On this shoulder is supported an inner shoulder of a bush(193) surrounding the mobile part (192). Rotating this bush (193) thenlocks the moving part (192) by tightening its conical surface (196)against the conical surface (197) of the stationary part (191) owing toa thread carried by this same bush (193) and engaging with a threadcarried by this same stationary part (191).

In order to be able to be adjusted easily according to one or morepre-set angled positions, the moving part (192) comprises a cam (194)having one or more sides (194 a, 194 c), with radial surfaces, whichengage with one or more stop components (194 b, 194 d) integral with thestationary part (191) in order to form one or more stops. Depending onthe relative position of the sides (194 a, 194 c) and stop components(194 b, 194 d), one or more pre-set angled positions are selectable inthis way, simply by loosening the bush (193) before swiveling the movingpart (192) as far as one of the stops then re-tightening the bush.

In another embodiment, the moving part (192) has an annular surface(195) with the approximate shape of a disk portion perpendicular to theaxis of inclination (d19) and having on its surface facing towards thestationary part (191) one or more depressions (195 c). On this annularsurface (195) a ball (195 a) maintained in a blind indent integral withthe stationary part (191) is pressed by the action of a spring (195 b)compressed into this same indent. When the moving part (192) is rotatedrelative to the stationary part (191), a ball (195 a) opposite adepression (195 c) centers itself in it under the action on the spring(195 b) and thus determines a precise angled position. The presence ofone or more balls and one or more depressions thus makes it possible todefine a pre-set number of pre-set angled positions of the moving part(192) relative to the stationary part (191).

Such a device thus makes it possible to vary rapidly the angle of theprinthead (14), without the necessity for further adjustment duringthese modifications, and thus to adapt print resolution to currentproduction needs in a flexible, fast and accurate way, particularly whenthe change of substrate, for example between “open” and “closed”,requires a change of resolution in order to preserve the best possibleprint quality while avoiding some of the problems due to coalescence orto the size of the drops before drying.

The device according to the invention is controlled by a control system(3) comprising a computer, for example of the compatible personalcomputer type. This system receives signals from the ink level sensors(18, 28) or pressure sensors (22 a, 22 b) or both of these, and controlsthe means (21 a, 21 b, 21 c) for adjusting the compressed air supplypressure or the cut-off means (17) or the distribution means (15) or thenon-return means (16) or a combination of these components, by means ofat least one electronic interface. In one embodiment, all the functionsand signals of the printed module (1) are managed by one electronicinterface (31) of a known type, this electronic interface communicatingwith the control system (3) by a series connection (c30) operating forexample according to the Universal Serial Bus computing standard. Usingsuch a connection then enables easy replacement of the control system(3) or the print module (1), for example for reasons of maintenance,system updating, or for replacing one print module by another comprisingdifferent settings or having different performance.

It must be obvious for those skilled in the art that the presentinvention allows embodiments in a number of other specific forms withoutdeparting from the field of application of the invention as claimed.Consequently, the present embodiments must be considered as examples,but may be modified in the field defined by the scope of the attachedclaims, and the invention must not be restricted to the details givenabove.

1. Digital device for printing on “open” or “closed” surface substratesby demand bubble-jet comprising at least one built-in ink reservoir witha system of anti-splash partitions, at least one printhead and onebuffer reservoir, the whole located in a print module which moves inrelation to the substrate, characterized in that it comprises means forcreating, during operation of said print module, on the one hand, avacuum in the built-in reservoir, and, on the other hand, an airpressure in the built-in reservoir for printhead cleaning phases, activeregulation means for regulating said vacuum by adjustment of thebuilt-in reservoir ink level and a sensor attached to the built-inreservoir for detecting the ink level and controlling flow of ink intothe built-in ink reservoir.
 2. Device of claim 1, wherein said printheadincludes nozzles and further comprising a means for pressurizing the airin the reservoir for cleaning the printhead nozzle(s).
 3. Device ofclaim 1, characterized in that said regulation means comprises anon-contact sensor for measuring the ink level, without contact with theink, through a wall of the built-in reservoir, the said sensor beingconnected to means for cutting off the ink flow by interrupting thesupply of ink to the built-in reservoir, said means for cutting off theink being controlled by a circuit receiving level signals from thenon-contact sensor in order to regulate the level of ink in thereservoir.
 4. Device of claim 1, characterized in that said activeregulation means for actively regulating the vacuum comprises apneumatic system consisting of a means for measuring the amount ofvacuum and a means for creating a vacuum, and an electronic circuit forcontrolling pressure according to ink system supply solenoid valvecontrol signals, air system solenoid valve control signals and signalsfrom the level sensor.
 5. Device of claim 1, characterized in that saidmeans for creating a vacuum use a venturi effect.
 6. Device of claim 1,characterized in that said means for creating a vacuum include aregulated vacuum pump.
 7. Device of claim 4, characterized in that saidprint module comprises a “buffer reservoir for storing a certainquantity of air at high or low pressure, said buffer reservoir smoothingout pressure variations occurring in pneumatic system.
 8. Device ofclaim 1, characterized in that said built-in reservoir comprises astorage space containing several separators dividing said storage spaceinto several areas covering at least a part of the height of thereservoir, said areas having a horizontal section of the order of 1 cm²,to reduce splashing of the ink.
 9. Device of claim 8, characterized inthat said separators comprise a number of inter-locked verticalpartitions.
 10. Device of claim 2, characterized in that for the nozzlecleaning, a flexible blade is placed in position in contact with theprinthead equipped with the nozzles and means of movement cause theprinthead to move in relation to the flexible blade in such a manner asto wipe the nozzle.
 11. Device of claim 1, characterized in that a printmodule moves in relation to a stationary control bay and most of the airpressure used in the print module comes from the control bay via atleast one flexible hose having sufficient length to allow movement ofthe print module.
 12. Device of claim 3, characterized in that said wallof the ink reservoir has a portion with a reduction in thickness forminga thinner part near the sensor so as to enable improved operation of theink level sensor through said thinner part, the reduction in thicknessbeing such that the thickness of said wall at this point is less than 1mm.
 13. Device of claim 1, characterized in that at least one printheadcarries a number of print nozzles arranged in preset positions in a rowinclined at an angle to a plane at right-angles to the direction oftravel of said printhead in relation to the substrate, and furtherincluding means for adjusting said angle, said means for adjustmentdetermining several preset positions enabling a change from one toanother without requiring further adjustment of the angle and withoutaltering the adjustment of said preset positions.
 14. Device of claim13, characterized in that said various preset positions correspond toangled positions making it possible with same spacing of the printnozzles on the printhead to print according to preset resolutions byvarying spacing of the dots printed on the substrate, the spacing of thedots decreasing as the angle increases.
 15. Device of claim 10,characterized in that said means of movement move at least one“cleaning” blade, adapted to be soaked in a solvent or rubbed on anabsorbent felt before scraping the printhead, and the means of movementmoves at least one other “wiping” blade, scraping an outer surface ofthe printhead after passage of the cleaning blade.
 16. Device of claim1, characterized in that it includes a data processing control systemreceiving signals from at least one ink level sensor or pressure sensoror both, and controlling one or more components including a compressedair supply pressure adjustment component or an ink cut-off component oran air distribution component or an air non-return component or acombination of said components, via at least one electronic interface.17. Device of claim 16, characterized in that said print module includesan electronic interface communicating with the control system via aseries connection.
 18. Device of claim 10, characterized in that itincludes a drain tray, positioned in front of the head to receive inkejected from the head during purging operations.